Update model cache for MultimodalQnA (opea-project#1618)

Signed-off-by: ZePan110 <[email protected]>

Author: ZePan110

MultimodalQnA/tests/test_compose_on_rocm.sh

@@ -9,6 +9,7 @@ echo "REGISTRY=IMAGE_REPO=${IMAGE_REPO}"
 echo "TAG=IMAGE_TAG=${IMAGE_TAG}"
 export REGISTRY=${IMAGE_REPO}
 export TAG=${IMAGE_TAG}
+export MODEL_CACHE=${model_cache:-"/var/lib/GenAI/data"}
 
 WORKPATH=$(dirname "$PWD")
 LOG_PATH="$WORKPATH/tests"